Yttrium-90-labeled monoclonal antibody for therapy: labeling by a new macrocyclic bifunctional chelating agent

Yttrium-90 (⁹⁰Y) is a promising radiometal for therapy of cancer due to its high-energy beta emission and a physical half-life of 2.67 days. Bifunctional chelating agents based on DTPA cyclic anhydride or EDTA do not form Y(III) complexes that are stable under physiologic conditions. A new macrocyclic bifunctional chelating agent based on 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) forms a stable Y(III) complex. It was converted to p-bromoacetamidobenzyl-DOTA (BAD), and conjugated to monoclonal antibody Lym-1 via 2-iminothiolane, either as the free ligand or as the ⁸⁸Y chelate. Stability studies of Lym-1-2IT-BAD-⁸⁸Y in human serum in vitro showed no measurable loss of Y(III) from the ligand over a 25-day period. In Raji-tumored mice, tumor uptake was 16.8% of the injected dose per gram of tissue on Day 3. The bone uptake was 2.0, 3.6, and 2.1% injected dose per gram of tissue on Day 1, 3, and 5, respectively. The biodistribution of the control ⁸⁸Y-citrate demonstrated continuous increase in bone uptake from 13.8% injected dose per gram on Day 1 to 24.9% injected dose per gram on Day 4.